Conventional pneumatic tires for utility vehicles usually have a four-ply belt with what is referred to as a triangular configuration in which two working plies are arranged one on top of the other in the radial direction, the steel cords of which are at an angle of approximately 15° to 30° with respect to the circumferential direction, wherein the steel cords of the one working ply and those of the second working ply are inclined in different axial directions A. As a result, the working plies form a diagonal assembly. In such belts there is usually a belt ply embodied as a barrier ply which is located under the working plies, the steel cords of which are at an angle of 45° to 60° with respect to the circumferential direction, as a result of which the cords of the working plies and of the barrier ply form a triangular assembly. In addition, usually an additional protective ply which forms the fourth belt ply is formed above the two working plies, the steel cords of which protective ply are also at an angle of approximately 45° to 30° with respect to the circumferential direction of the vehicle tire. Such belts have a limited circumferential strength. The possibility of moving the belt edges, which this provides, can have an adverse effect on the durability of the tire. The belt can also be subject to radial expansion during operation. This growth can lead to excessive unequal wear of the tire.
It is also known to form pneumatic tires for utility vehicles with a four-ply arrangement with a radially inner barrier ply with steel cords which enclose an angle of approximately 45° to 65° with respect to the circumferential direction, with two working plies which are formed over the barrier ply and which form in a conventional way a diagonal assembly of their steel cords with an orientation of the steel cords of in each case approximately 15° to 30°, and with a fourth belt ply which is formed radially outside the two working plies on the outer working ply and which is embodied as what is referred to as a zero-degree ply, wherein the reinforcement members thereof composed of steel cords are oriented essentially in the circumferential direction with an angle of 0° to 2.5° with respect to the circumferential direction. In such formations, the circumferential strength of the belt is increased, which has a positive effect on the durability of the belt. However, the influence of the zero-degree ply is limited essentially to the radially outer working ply. However, the inner working ply is formed with residual mobility, still with adverse effects on the durability and wear.
Furthermore, occasionally a formation of a pneumatic tire for a utility vehicle with a belt arrangement in which a zero-degree ply is formed radially between the two working plies has been proposed. The two working plies continue to be formed in the diagonal assembly in these proposed embodiments and their steel cords are oriented with angles of, in each case, approximately 18° with respect to the circumferential direction. In point of fact, this embodiment permits a high level of circumferential strength and improved durability and an improved wear performance compared to a conventional pneumatic tire for a utility vehicle. The steel cords of these known working plies are usually steel cords of the type 3×0.20+6×0.35NT. So that these steel cords, which have a breaking strength F of 1700N and an extension of less than 0.15% at 10% of the breaking strength, maintain a sufficient puncture resistance, a multiplicity of steel cords with relatively thin cross section are formed with a high arrangement density in the working plies. Steel cords with a large cross sectional thickness, which would promote the belt durability, are as a result usable only to a limited degree. Even if they were used, they give rise to the high arrangement density which is necessary to limit the risk of puncturing, large belt ply weight, large quantities of material and a negative influence on the wear.
U.S. Pat. No. 5,772,810 A discloses a pneumatic tire for a utility vehicle, having a belt ply design with a zero degree ply which is embodied between two working plies with such non extendable reinforcement members. In U.S. Pat. No. 5,772,810 A, it is proposed to couple the working plies outside the zero degree ply in order to overcome the problems associated with these belt ply designs with non extendable reinforcement members, these problems involving restricted belt durability due to belt edge movement of the non extendable reinforcement members.
United States patent application publication 2012/0318426 discloses a pneumatic tire for a utility vehicle, having a belt arrangement with another belt design with a zero degree ply which is embodied radially between the two working plies. The two working plies are also embodied in the diagonal assembly. The reinforcement members of the two working plies are extendable with an extension D of 0.22%≦D≦0.4% at 10% of the breaking strength. The pneumatic tire for a utility vehicle, which is known from this publication, enables, through this embodiment with extendable reinforcement members, a significantly improved belt durability by utilizing the advantages of the arrangement of the zero degree ply between the working plies in contrast with the previously known pneumatic tires for a utility vehicle having belts whose reinforcement members of the working plies are embodied with non extendable reinforcement members.